CN110868258B

CN110868258B - Device, system and method for realizing coherent detection

Info

Publication number: CN110868258B
Application number: CN201810979514.4A
Authority: CN
Inventors: 涂芝娟; 张俊文; 黄新刚; 李明生
Original assignee: ZTE Corp
Current assignee: ZTE Corp
Priority date: 2018-08-27
Filing date: 2018-08-27
Publication date: 2022-08-16
Anticipated expiration: 2038-08-27
Also published as: WO2020043096A1; EP3846360A1; US20210320723A1; CN110868258A; EP3846360A4; US11569916B2

Abstract

The embodiment of the invention discloses a device, a system and a method for realizing coherent detection, wherein the device comprises: a first transceiving unit, configured to send a first-direction optical signal to a second device, where the first-direction optical signal includes a direct-current first wavelength optical signal and a modulated second wavelength optical signal; and receiving a second directional optical signal from a second device, the second directional optical signal comprising a modulated first wavelength optical signal; and the first coherent receiver is connected to the first transceiver unit, and configured to perform coherent mixing on a part of the direct-current first wavelength optical signal in the first-direction optical signal as coherent received local oscillation light and the second-direction optical signal, and demodulate the second-direction optical signal. In the embodiment of the invention, the coherent receiving local oscillator laser is saved, and the coherent detection cost and complexity are reduced.

Description

Device, system and method for realizing coherent detection

Technical Field

The present application relates to the field of optical communication technologies, and in particular, to an apparatus, a system, and a method for implementing coherent detection.

Background

At present, coherent detection technology has become an important development direction of optical communication systems. Power budget and cost are two important considerations for building optical communication systems. Due to the introduction of Local Oscillator (LO) light, the coherent detection technology can significantly improve the receiving sensitivity of the system and reduce the power requirement for receiving signal light, thereby alleviating the problem of bandwidth and power limitation of the conventional optical communication system.

The main components of a coherent receiver specified in the Optical Internet Forum (OIF) standard are shown in fig. 1. For a coherent detection system, a local oscillator laser needs to be introduced to provide local oscillator light. In order to realize coherent detection with maximum sensitivity, the signal light and the local oscillator light need to satisfy the following conditions: the polarization state is the same, the frequency is the same or the frequency difference is kept stable, and the phase noise is limited. Therefore, in order to keep the center wavelength of the signal light consistent, it is necessary to use a highly accurate tunable laser as a local oscillation light source for coherent detection. In order to reduce the phase noise, the linewidth of the local oscillator laser used is also required to be extremely narrow, which results in high cost and high price of the coherent detection system.

Disclosure of Invention

The embodiment of the invention provides a device, a system and a method for realizing coherent detection, which are used for reducing the cost and complexity.

The embodiment of the invention provides a device for realizing coherent detection, which comprises:

a first transceiving unit, configured to send a first-direction optical signal to a second device, where the first-direction optical signal includes a direct-current first wavelength optical signal and a modulated second wavelength optical signal; and receiving a second directional optical signal from a second device, the second directional optical signal comprising a modulated first wavelength optical signal;

and the first coherent receiver is connected to the first transceiver unit, and configured to perform coherent mixing on a part of the direct-current first wavelength optical signal in the first-direction optical signal as coherent received local oscillation light and the second-direction optical signal, and demodulate the second-direction optical signal.

The embodiment of the present invention further provides an apparatus for implementing coherent detection, including:

a second transceiving unit, configured to receive a first-direction optical signal from a first device, where the first-direction optical signal includes a direct-current first-wavelength optical signal and a modulated second-wavelength optical signal;

and the second coherent receiver is connected to the second transceiver unit, and configured to perform coherent mixing on a part of the direct-current first wavelength optical signal as coherent received local oscillation light and the modulated second wavelength optical signal, and demodulate the modulated second wavelength optical signal.

The embodiment of the invention also provides a system for realizing the coherent detection, which comprises a first device and a second device connected with the first device through an optical fiber link, wherein the second device is connected with the first device through the optical fiber link

Said first device comprises said coherent detection means;

the second device comprises the coherent detection apparatus.

The embodiment of the invention also provides a method for realizing the coherent detection, which comprises the following steps:

a first device sends a first direction optical signal to a second device, wherein the first direction optical signal comprises a direct current first wavelength optical signal and a modulated second wavelength optical signal;

the first device receives a second-direction optical signal from the second device, performs coherent mixing on a part of a direct-current first-direction optical signal in the first-direction optical signal as coherent-received local oscillation light and the second-direction optical signal, and demodulates the second-direction optical signal; wherein the second direction optical signal comprises a modulated first wavelength optical signal.

the second device receives a first direction optical signal from the first device, wherein the first direction optical signal comprises a direct current first wavelength optical signal and a modulated second wavelength optical signal;

and the second device performs coherent mixing on a part of the direct-current first wavelength optical signal as coherent received local oscillation light and the modulated second wavelength optical signal, and demodulates the modulated second wavelength optical signal.

and the second device receives the first-direction optical signal from the first device, performs coherent mixing on a part of the direct-current first-wavelength optical signal as coherent received local oscillation light and the modulated second-wavelength optical signal, and demodulates the modulated second-wavelength optical signal.

The embodiment of the invention comprises the following steps: a first device sends a first-direction optical signal to a second device, wherein the first-direction optical signal comprises a direct-current first-wavelength optical signal and a modulated second-wavelength optical signal; and the second device receives the first-direction optical signal from the first device, performs coherent mixing on a part of the direct-current first-wavelength optical signal as coherent received local oscillation light and the modulated second-wavelength optical signal, and demodulates the modulated second-wavelength optical signal. In the embodiment of the invention, the coherent receiving local oscillator laser is saved, and the coherent detection cost and complexity are reduced.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the example serve to explain the principles of the invention and not to limit the invention.

Fig. 1 is a schematic diagram of the main components of a coherent receiver specified in the OIF standard;

FIG. 2 is a schematic diagram of a system for implementing coherent detection according to an embodiment of the present invention;

fig. 3 is a schematic diagram of an implementation apparatus of coherent detection according to an embodiment of the present invention (applied to a first device);

fig. 4 is a schematic diagram illustrating a first transceiver unit according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of the first apparatus according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of the first apparatus according to another embodiment of the present invention;

FIG. 7 is a schematic diagram of the first apparatus according to still another embodiment of the present invention;

FIG. 8 is a schematic diagram of a first coherent receiver according to an embodiment of the present invention;

FIG. 9 is a schematic diagram of an apparatus for implementing coherent detection according to an embodiment of the present invention (applied to a second device);

fig. 10 is a schematic diagram illustrating a second transceiver unit according to an embodiment of the present invention;

FIG. 11 is a schematic diagram of a second apparatus according to an embodiment of the present invention;

FIG. 12 is a schematic diagram of the second apparatus according to another embodiment of the present invention;

FIG. 13 is a schematic diagram of the second apparatus according to still another embodiment of the present invention;

fig. 14(a) to (c) are schematic diagrams showing the composition of a second optical transmitter according to an embodiment of the present invention;

fig. 15 is a block diagram of a second coherent receiver according to an embodiment of the present invention;

fig. 16 is a schematic diagram of a second coherent receiver according to another embodiment of the present invention;

FIG. 17 is a diagram illustrating a system for implementing coherent detection according to an embodiment of the present invention;

FIG. 18 is a schematic diagram of a system for implementing coherent detection according to another embodiment of the present invention;

fig. 19 is a flowchart illustrating a method for implementing coherent detection according to an embodiment of the present invention (applied to a first device);

fig. 20 is a flowchart illustrating a method for implementing coherent detection according to another embodiment of the present invention (applied to a first device);

FIG. 21 is a sub-flowchart of an implementation method of the coherent detection shown in FIG. 19 or FIG. 20 according to an embodiment of the present invention;

FIG. 22 is a schematic sub-flowchart of an implementation method of the coherent detection shown in FIG. 19 or FIG. 20 according to an embodiment of the present invention;

fig. 23 is a flowchart illustrating a method for implementing coherent detection according to an embodiment of the present invention (applied to a second device);

FIG. 24 is a flow chart of a method for implementing coherent detection according to another embodiment of the present invention (applied to a second device);

fig. 25 is a schematic flow chart of a method for implementing coherent detection according to an embodiment of the present invention (applied to a system for implementing coherent detection);

fig. 26 is a flowchart of a method for implementing coherent detection according to another embodiment of the present invention (applied to a system for implementing coherent detection).

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.

In order to reduce the cost of the system, in the coherent detection system, a part of the modulation signals can be used as local oscillator light after being subjected to data erasure by a certain technical means, so that a local oscillator laser is saved. However, this scheme requires the introduction of an additional envelope detector, a semiconductor optical amplifier, a narrow-band optical filter, etc., which increases the complexity and cost of the system, and makes it difficult to completely erase the modulated signal. In addition, since the polarization state of the signal light is random after being transmitted through the common optical fiber, the coherent receiver usually adopts the polarization diversity method shown in fig. 1 to respectively receive two polarization state components of the optical signal, so that the complexity of the coherent receiver is doubled, and the cost of the coherent detection system is greatly increased.

In addition, since the Signal light and the local oscillator light are respectively derived from different lasers, it is difficult to achieve stable and accurate matching of frequency and phase, and after Analog-to-Digital Converter (ADC) is performed, a Digital Signal Processing (DSP) algorithm is still required to correct frequency and eliminate phase noise, thereby further increasing the complexity of the coherent detection system. Therefore, the cost and system complexity problem is an important factor that affects the inability of the coherent detection technology to scale in Passive Optical Network (PON) systems.

The embodiment of the invention provides a device, a system and a method for realizing coherent detection, which can simplify the structure and reduce the cost.

Fig. 2 shows a schematic composition diagram of a system for implementing coherent detection according to an embodiment of the present invention, which includes a first device 10 and a second device 20 connected to the first device 10 through an optical fiber link 30.

The first device 10 sends a first-direction optical signal (indicated by a solid line) to the second device 20, where the first-direction optical signal includes a direct-current first-wavelength optical signal λ 1 and a modulated second-wavelength optical signal λ 2 (S). The second device 20 sends a second directional optical signal (indicated by dashed lines) comprising the modulated first wavelength optical signal λ 1(S) to the first device 10.

The first device 10 generates optical signals λ 1, λ 2 with two wavelengths in a first direction, modulates the optical signal with one of the wavelengths to obtain λ 2(S), and splits a part of the direct current light λ 1; when the light beam arrives at the second direction λ 1(S), coherent mixing is directly performed with the split local oscillation light λ 1, so that coherent reception is realized.

After the optical signals λ 1 and λ 2(S) in the first direction arrive, the second device 20 splits the light with two wavelengths, and splits the direct current light λ 1 into two parts, one part is used as local oscillation light, and performs coherent mixing with the modulated optical signal λ 2(S) with the second wavelength in the first direction, so as to implement coherent reception. The other part of the direct current light is modulated, reflected and the like to generate a second direction optical signal, i.e. a modulated first wavelength optical signal λ 1 (S).

The embodiment of the present invention may be applied to, but not limited to, a PON system, where the first device 10 may be an OLT (Optical Line Terminal), the second device 20 may be an ONU (Optical Network Unit), the first direction may be a downlink direction, and the second direction may be an uplink direction. The OLT and the ONUs are connected via an ODN (Optical Distribution Network).

The first device 10 side and the second device 20 side are described below, respectively.

As shown in fig. 3, for the first device 10 side, an apparatus for implementing coherent detection is located in the first device 10, and includes:

a first transceiving unit 11, configured to send a first-direction optical signal to a second device 20, where the first-direction optical signal includes a direct-current first wavelength optical signal and a modulated second wavelength optical signal; and receiving a second directional optical signal from a second device 20, the second directional optical signal comprising a modulated first wavelength optical signal;

a first coherent receiver 12, connected to the first transceiver, configured to perform coherent frequency mixing on a part of the direct-current first wavelength optical signal in the first direction optical signal as coherently received local oscillation light with the second direction optical signal, and demodulate the second direction optical signal.

In the embodiment of the invention, the coherent receiving local oscillator laser is saved, and the coherent detection cost and complexity are reduced.

As shown in fig. 4, in an embodiment, the first transceiver unit 11 includes a first optical transmitter 111, a modulation separation subunit 112 and an interface subunit 113 connected in sequence, wherein

The first optical transmitter 111 is configured to generate an optical signal to be modulated, where the optical signal to be modulated includes a direct-current first wavelength optical signal and a direct-current second wavelength optical signal;

the modulation and separation subunit 112 is configured to modulate a direct-current second wavelength optical signal in the optical signal to be modulated into a modulated second wavelength optical signal;

the interface subunit 113 is configured to send a first-direction optical signal to the second device 20 by using the direct-current first-wavelength optical signal and the modulated second-wavelength optical signal as first-direction optical signals, receive a second-direction optical signal from the second device 20, and send the second-direction optical signal to the first coherent receiver 12.

In the embodiment of the invention, the optical signal in the second direction adopts two wavelengths, so that one path of signal modulation can be realized at the same time, and one path of direct current light is directly used as local oscillator light.

Referring to fig. 5, in an embodiment, the first optical transmitter 111 includes a dual-wavelength laser 1111, and the dual-wavelength laser 1111 is configured to generate the optical signal to be modulated.

The light emitted from the dual-wavelength laser 1111 includes two wavelengths with a constant frequency difference, and if the environment changes, the two wavelengths change simultaneously, but the frequency difference remains constant.

Because two wavelengths in the optical signal in the first direction come from the same laser, the frequency difference is constant and adjustable, the wavelength of the local oscillation light does not need to be continuously adjusted along with the change of the environment and the temperature, the complexity of the realization and the operation of the system is reduced, and the large-scale application is favorably realized. The Laser can be realized by adopting, but not limited to, a Distributed Feedback Laser (DFB) based on sampling grating period adjustment, and can also be realized by adopting, but not limited to, a dual-wavelength semiconductor Laser based on a V-type coupling cavity.

Referring to fig. 5, in an embodiment, the modulation separation subunit 112 includes a first wave splitter 1121, a first light modulator 1122, and a wave combiner 1123 connected in sequence, wherein

The first wave splitter 1121 is configured to split the optical signal to be modulated into two light beams, where one light beam is a direct-current first wavelength optical signal, and the other light beam is a direct-current second wavelength optical signal; sending a part of the direct current optical signal with the first wavelength to the coherent receiver 12, and sending the other part to the combiner 1123; sending a beam of direct second wavelength optical signals to the first optical modulator 1122;

the first optical modulator 1122 is configured to modulate the received direct-current second wavelength optical signal into a modulated second wavelength optical signal, and send the modulated second wavelength optical signal to the combiner 1123;

the combiner 1123 is configured to combine the received direct-current first wavelength optical signal and the modulated second wavelength optical signal into one optical beam, and send the optical beam to the interface subunit 113.

The first wave splitter 1121 and the wave combiner 1123 may use the same device, may realize an optical demultiplexing/multiplexing function, may use, but are not limited to, an Arrayed Waveguide Grating (AWG), and may also be realized by a structure such as a micro-ring resonator.

The first optical modulator 1122 may implement modulation of an optical signal in a first direction, and may be implemented by, but not limited to, an electro-absorption (EA) modulator, a Mach-Zehnder (MZ) modulator, a micro-ring modulator, and the like, and different optical modulation devices may be selected according to a modulation format required by a system in an actual implementation manner.

Referring to FIG. 5, in one embodiment, the interface subunit 113 may include an optical circulator 1131.

In fig. 5, the working process of the implementation apparatus for coherent detection includes: the dual-wavelength laser 1111 emits a light signal containing two wavelengths λ 1 and λ 2, and the frequency difference between λ 1 and λ 2 is kept constant. An optical signal emitted by the dual-wavelength laser 1111 is split into two paths with wavelengths λ 1 and λ 2 by the first splitter 1121. The optical signal with the wavelength λ 2 is loaded with a modulation signal through the first optical modulator 1122, and a modulated λ 2(S) modulated signal light is output. The optical signal with the wavelength λ 1 may be divided into two parts by a power splitter, one part is used as coherent received local oscillation light λ 1(LO) in the second direction, the other part and λ 2(S) modulated signal light are combined into one optical signal (i.e., a first-direction optical signal) by the combiner 1123, and the first-direction optical signal is output after passing through the optical circulator 1131, enters the optical fiber link 30 for transmission and power distribution, and is sent to the second device 20.

After the optical signal λ 1(S) (indicated by a dashed arrow) in the second direction reaches the first device 10 via the optical fiber link 30, the optical signal is input into the first coherent receiver 12 through the optical circulator 1131, and can be input into the first coherent receiver 12 together with the local oscillator light λ 1(LO), so as to implement coherent reception of the optical signal in the second direction.

Referring to fig. 6, in an embodiment, the first optical transmitter 111 includes a single-wavelength laser 1112, an rf source 1113, and a second optical modulator 1114, wherein the single-wavelength laser 1112 is connected to the second optical modulator 1114, and the second optical modulator 1114 is connected to the rf source 1113 and the modulation and separation subunit 112, respectively;

the single-wavelength laser 1112 is configured to generate a single-wavelength optical signal, and send the single-wavelength optical signal to the second optical modulator 1114;

the second optical modulator 1114 is configured to modulate the single-wavelength optical signal under the driving of the rf source 1113, generate the optical signal to be modulated, and send the optical signal to the modulation and separation subunit 112.

In this embodiment, the first optical transmitter 111 is based on a commonly used single wavelength laser. The single-wavelength Laser 1112 may be implemented by, but not limited to, a conventional DFB Laser, an External Cavity Laser (ECL), a Fabry-Perot (FP) Laser, or the like.

The second optical modulator 1114 mainly implements a function of generating a plurality of wavelengths driven by a radio frequency signal, and may be implemented by, but not limited to, an intensity modulator, a phase modulator, and an In-phase Quadrature (IQ) modulator. In actual operation, the number of wavelengths and the wavelength interval can be adjusted by changing the frequency and waveform of the rf signal, the bias point of the second optical modulator 1114, the driving voltage, and other factors, so as to obtain different frequency components.

If more than two wavelengths are generated after passing through the second optical modulator 1114, then the tunable filter 1115 can be selected to obtain both wavelengths λ 1 and λ 2. Referring to fig. 6, in another embodiment, the first optical transmitter 111 comprises a single-wavelength laser 1112, an rf source 1113, a second optical modulator 1114 and a tunable filter 1115, wherein the single-wavelength laser 1112 is connected to the second optical modulator 1114, the second optical modulator 1114 is connected to the rf source 1113 and the tunable filter 1115, respectively, and the tunable filter 1115 is connected to the modulation separation subunit 112;

the second optical modulator 1114 is configured to modulate the single-wavelength optical signal by driving the radio frequency source 1113, and generate optical signals with two or more wavelengths including the direct-current first-wavelength optical signal and the direct-current second-wavelength optical signal;

the adjustable filter 1115 is configured to filter the optical signals with the two or more wavelengths to obtain the optical signal to be modulated, and send the optical signal to the modulation separation subunit 1112.

In fig. 6, the working process of the implementation apparatus for coherent detection includes: the single-wavelength laser 1112 emits light with a wavelength λ and inputs the light into the second optical modulator 1114, the second optical modulator 1114 generates a bundle of optical signals with two wavelengths λ 1 and λ 2 and known frequency difference under the driving of the radio frequency signal (or the second optical modulator 1114 generates a bundle of optical signals with multiple (greater than or equal to two) wavelengths under the driving of the radio frequency signal, and then obtains the optical signals with two wavelengths λ 1 and λ 2 and known frequency difference through the tunable filter 1115), and then the optical signals are split into two paths of optical signals with wavelengths λ 1 and λ 2 through the first splitter 1121. The optical signal with the wavelength λ 2 is loaded with a modulation signal through the first optical modulator 1122, and a modulated λ 2(S) modulated signal light is output. An optical signal with a wavelength of λ 1 may be divided into two parts by a power splitter, where one part is used as coherent received local oscillation light λ 1(LO) in the second direction, the other part and λ 2(S) modulated signal light are combined into one optical signal (i.e., a first-direction optical signal) through the combiner 1123, and the first-direction optical signal is output after passing through the optical circulator 1131, enters the optical fiber link 30, is transmitted and power-distributed, and is sent to the second device 20.

After the optical signal λ 1(S) in the second direction reaches the first device 10 via the optical fiber link 30, the optical signal is input into the first coherent receiver 12 through the optical circulator 1131, and may be input into the first coherent receiver 12 together with the local oscillator light λ 1(LO), so as to implement coherent reception of the optical signal in the second direction.

As shown in fig. 7, in an embodiment, the first transceiver unit 11 further includes a polarization rotator 114.

The polarization rotator 114 is respectively connected to the first coherent receiver 12 and the interface subunit 113, and is configured to perform polarization conversion on the optical signal in the second direction, and send the optical signal to the first coherent receiver 12.

When the second device performs polarization processing on the optical signal in the second direction, the polarization rotator 114 may perform polarization conversion on the received optical signal in the second direction, so that the local oscillation light and the optical signal in the second direction have the same polarization state.

In another embodiment, when the second device performs polarization processing on the optical signal in the second direction, the first device 10 does not perform polarization processing on the received optical signal in the second direction, but performs polarization processing on the local oscillator light, so that the local oscillator light and the optical signal in the second direction have the same polarization state. Then in this embodiment, the polarization rotator 114 is located between the modulation separation subunit 112 and the first coherent receiver 12, and performs polarization processing on the local oscillator light output by the modulation separation subunit 112.

Referring to fig. 3, 5, 6 and 7, the first coherent receiver 12 can implement coherent reception of the optical signal in the second direction to improve the reception sensitivity in the second direction. Since the polarization state of the second-direction optical signal may change after passing through the optical fiber link 30 (e.g., ODN) and the optical circulator, the first coherent receiver 12 may receive two polarization state components of the second-direction optical signal respectively based on a polarization diversity structure commonly used in the optical communication field. Since the local oscillator light coherently received by the first device 10 is from the laser in the first optical transmitter 111, the expensive local oscillator laser is saved, and the cost of the device is reduced. In addition, because the wavelengths of the signal light and the local oscillator light are lambda 1, homodyne reception is easy to realize, the complexity of a DSP algorithm is reduced, and the system is simple and easy to realize.

The first coherent receiver 12 may also be based on the structure of other coherent receivers that are insensitive to the polarization of the signal light and the local oscillator light. Taking coherent reception of intensity modulated signals as an example, referring to fig. 8, in one embodiment, the first coherent receiver 12 comprises: the optical coupler comprises a first optical coupler 121, a polarization beam splitter 122, a first photodetector 123, a second photodetector 124 and a signal processing module 125, wherein the polarization beam splitter 122 is respectively connected with the first optical coupler 121, the first photodetector 123 and the second photodetector 124, the signal processing module 125 is respectively connected with the first photodetector 123 and the second photodetector 124, and the signal processing module 125 is respectively connected with the first photodetector 123 and the second photodetector 124, wherein

The first optical coupler 121 is configured to perform coherent frequency mixing on the local oscillator light and the optical signal in the second direction to generate a mixed optical signal;

the polarization beam splitter 122 is configured to split the mixed optical signal into two polarized optical signals in two directions, send the polarized optical signal polarized in the X direction to the first photodetector 123, and send the polarized optical signal polarized in the Y direction to the second photodetector 124;

the first photodetector 123 is configured to convert the polarized light signal polarized in the X direction into a first electrical signal, and send the first electrical signal to the signal processing module 125;

the second photodetector 124 is configured to convert the polarized optical signal polarized in the Y direction into a second electrical signal, and send the second electrical signal to the signal processing module 125;

the signal processing module 125 is configured to perform digital signal processing on the first electrical signal and the second electrical signal, so as to demodulate the second directional optical signal.

In this embodiment, this polarization insensitive first coherent receiver 12 can achieve polarization insensitive reception of an intensity modulated signal by using several simple devices as shown in fig. 8, compared to a polarization diversity coherent receiver. The first optical coupler 121 mixes the signal light and the local oscillator light, and may be implemented by, but not limited to, a 3dB coupler. The signal processing module 125 can perform square rate detection, filtering, and electrical signal addition on the two electrical signals output by the first photodetector 123 and the second photodetector 124, respectively, so as to implement demodulation processing on the modulated signal. The signal processing module 125 can be implemented based on, but not limited to, signal processing in the analog domain, and can also be implemented based on a simple DSP algorithm. The first coherent receiver 12 adopts a polarization insensitive coherent receiver structure, and can realize correct coherent reception and demodulation of the optical signal in the second direction without adopting a polarization diversity structure and a complex DSP algorithm, so that the complexity of the device is greatly reduced, and the cost of the device is further reduced.

For the second device 20 side, as shown in fig. 9, an apparatus for implementing coherent detection is located in the first device 20, and includes:

a second transceiving unit 21, configured to receive a first-direction optical signal from the first device 10, where the first-direction optical signal includes a direct-current first-wavelength optical signal and a modulated second-wavelength optical signal;

a second coherent receiver 22, connected to the second transceiver 21, configured to perform coherent mixing on a part of the direct-current first wavelength optical signal as coherent received local oscillation light and the modulated second wavelength optical signal, and demodulate the modulated second wavelength optical signal.

In an embodiment, the second transceiver unit 21 is further configured to modulate another part of the direct-current first-wavelength optical signal, generate a modulated first-wavelength optical signal, and send the modulated first-wavelength optical signal to the first device 10 as a second-direction optical signal.

In the embodiment of the invention, a laser for transmitting the optical signal in the second direction does not need to be additionally configured, so that the cost of the system is greatly reduced.

As shown in fig. 10, in an embodiment, the second transceiving unit 21 includes: a transceiver sub-unit 211 and a second optical transmitter 212 connected, wherein

The transceiver sub-unit 211 is configured to receive a first-direction optical signal from the first device 10, send a part of the direct-current first-wavelength optical signal to the second coherent receiver 22, and send another part of the direct-current first-wavelength optical signal to the second optical transmitter 212; and receiving the modulated optical signal of the first wavelength sent by the second optical transmitter 212, and sending the optical signal of the first wavelength to the first device 10;

the second optical transmitter 212 is configured to modulate another part of the direct-current first-wavelength optical signal to generate a modulated first-wavelength optical signal.

Referring to fig. 11, in an embodiment, the transceiver subunit 211 includes a signal splitting and amplifying module 2111, and the signal splitting and amplifying module 2111 includes a second wave splitter 21111 and an optical amplifier 21112 connected to each other, where

The second wave splitter 21111 is configured to split the optical signal in the first direction into two light beams, where one light beam is a direct-current first wavelength optical signal, and the other light beam is a modulated second wavelength optical signal; sending the direct-current first-wavelength optical signal to the optical amplifier 21112; sending the modulated second wavelength optical signal to the second coherent receiver 22;

the optical amplifier 21112 is configured to perform power amplification on the direct-current first-wavelength optical signal, send a part of the amplified direct-current first-wavelength optical signal to the second coherent receiver 22 as coherent received local oscillation light, and output the other part of the amplified direct-current first-wavelength optical signal to the second optical transmitter 212.

Referring to fig. 12, in another embodiment, the second splitter 21111 and the optical amplifier 21112 in the transceiver subunit 211 can be switched, and then the optical signal in the second direction is amplified and then split:

the optical amplifier 21112 is configured to perform power amplification on the first-direction optical signal, and output the first-direction optical signal to the second splitter 21111;

the second wave splitter 21111 is configured to split the amplified first-direction optical signal into two paths of light beams, where one path of light beam is a direct-current first-wavelength optical signal, and the other path of light beam is a modulated second-wavelength optical signal; a part of the direct-current first wavelength optical signal is output to the second coherent receiver 22 as coherent received local oscillation light, and another part of the direct-current first wavelength optical signal is output to the second optical transmitter 212; the modulated second wavelength optical signal is output to the second coherent receiver 22.

In the embodiments of fig. 11 and 12, the modulated optical signal of the first wavelength generated by the second optical transmitter 212 is power-amplified by the signal splitting and amplifying module 2111, and then output to the first device 10.

The second splitter 21111 may implement an optical demultiplexing function, which may be implemented by, but not limited to, an Arrayed Waveguide Grating (AWG), or may be implemented by, but not limited to, a micro-ring resonator or other structures.

The Optical Amplifier 21112 can realize the power amplification function of light, and can be realized by, but not limited to, a Semiconductor Optical Amplifier (SOA), and can also be realized by, but not limited to, an Erbium Doped Fiber Amplifier (EDFA).

In fig. 11, the working process includes: after the optical signal in the first direction (indicated by a solid arrow) transmitted and distributed through the optical fiber link 30 reaches a certain second device, the two optical signals having the wavelengths λ 1 and λ 2 are first separated by the second splitter 21111. λ 2(S) is input into the second coherent receiver 22, λ 1 is power-amplified by the optical amplifier 21112, and then is divided into two parts by the power splitter, and one part is input into the second coherent receiver 22 as local oscillation light λ 1(LO) together with the optical signal λ 2(S) of the second wavelength, so as to realize coherent reception of the optical signal in the first direction. Another part of the amplified λ 1 signal is input to the second optical transmitter 212, and λ 1(S) is output to the optical amplifier 21112 by applying a modulation signal to the λ 1 output λ 1(S) signal light (indicated by a dotted arrow). λ 1(S) power-amplified by the optical amplifier 21112 is input to the optical fiber link 30 via the second splitter 21111, and transmission and reception of the optical signal in the second direction are realized.

In fig. 12, the operation process includes: the first optical signal transmitted and distributed via the optical fiber link 30 first passes through the optical amplifier 21112, performs power amplification on λ 1 and λ 2(S) simultaneously, and then separates two optical signals having wavelengths of λ 1 and λ 2 by the second splitter 21111. Wherein λ 2(S) is input into the second coherent receiver 22, λ 1 is divided into two parts by the power beam splitter, and one part is input into the second coherent receiver 22 together with λ 2(S) as local oscillation light, so as to realize coherent reception of the optical signal in the first direction. Another part of the amplified λ 1 signal is input to the second optical transmitter 212, and the λ 1(S) signal light is output by applying a modulation signal to the λ 1 signal and input to the optical amplifier 21112 via the second splitter 21111. λ 1(S) power-amplified by the optical amplifier 21112 is input to the optical fiber link 30, and transmission and reception of the optical signal in the second direction are realized.

As shown in fig. 13, in an embodiment, the transceiver subunit 211 further includes a first interface module 2112 and a second interface module 2113, wherein

The first interface module 2112 is configured to output the first-direction optical signal to the signal separation and amplification module 2111, and send the modulated first-direction optical signal serving as a second-direction optical signal to the first device 10;

the second interface module 2113 is configured to output the direct-current first-wavelength optical signal output by the signal separation and amplification module 2111 to the second optical transmitter 212, and output the modulated first-wavelength optical signal output by the second optical transmitter 212 to the first interface module 2112.

In one embodiment, the first interface module 2112 and the second interface module 2113 each include an optical circulator.

The difference between fig. 11 and fig. 12 is that the modulated signal λ 1(S) output by the second optical transmitter 212 in fig. 13 is not amplified by an additional optical amplifier, and the modulated signal λ 1(S) can be input into the optical fiber link 30 by two optical circulators, so as to implement transmission and transmission of the optical signal in the second direction.

Referring to fig. 14(a), the second optical transmitter 212 includes a third optical modulator 2121, and the third optical modulator 2121 may be a reflective optical modulator.

The reflective optical modulator can modulate the optical signal with the first wavelength and reflect the modulated optical signal with the first wavelength to the same input optical fiber, and may be implemented by, but not limited to, an electro-absorption (EA) modulator plus a high-reflectivity coating or other reflector structures, and the implementation manner may be different optical modulation devices according to the modulation format required by the system. The SOA can be further integrated in the reflective optical modulator to amplify the modulated signal. The adoption of the reflective optical modulator can save a laser for emitting the optical signal in the second direction at the second equipment end, and reduce the cost of the equipment at the second equipment end.

Referring to FIG. 14(b), in one embodiment, the second optical transmitter 212 may further include a FP laser 2122, wherein

The FP laser 2122 is an injection-locked laser, and is configured to perform regenerative amplification on an input optical signal according to a frequency of the input direct-current first wavelength optical signal;

the third optical modulator 2121 is connected to the FP laser 2122 and the transceiver unit 211, and is configured to modulate the amplified direct-current first wavelength optical signal and output the modulated first wavelength optical signal.

In this embodiment, light generated by the injection-locked FP laser is modulated by the third modulator 2121 to generate the first wavelength optical signal λ 1 (S).

In this embodiment, the third modulator 2121 may be implemented by, but not limited to, an electro-absorption (EA) modulator, a mach-zehnder (MZ) modulator, a micro-ring modulator, etc., and different optical modulation devices may be selected according to a modulation format required by a system in an actual implementation manner.

The embodiment of fig. 14(b) is more suitable for use in conjunction with the embodiment of fig. 12.

Referring to fig. 14(c), on the basis of the embodiment of fig. 14(a), the second optical transmitter 212 further includes a faraday rotation mirror 2123.

The faraday rotation mirror 2123 is connected to the third optical modulator 2121, and configured to perform polarization processing on the modulated first wavelength optical signal output by the third optical modulator 2121, and output the modulated first wavelength optical signal subjected to polarization processing to the third optical modulator 2121.

In this embodiment, a First Rotating Mirror (FRM) 2123 is integrally pulled behind the reflective light modulator. The FRM has the effects that the polarization state of an optical signal rotates by 45 degrees after Faraday rotation for the first time, the polarization state can rotate by 45 degrees again in the same direction after Faraday rotation for the second time after reflection by a reflector, and therefore the polarization state of the input and output optical signals of the FRM can rotate by 90 degrees.

The second device 20 of the embodiment of fig. 14(c) is used in conjunction with the first device 10 of the embodiment of fig. 7.

Referring to fig. 9, the second coherent receiver 22 may implement coherent reception of the optical signal in the first direction to improve the receiving sensitivity in the first direction. Since the signal light and the local oscillator light input to the second coherent receiver 22 are from the same light source and transmitted through the same optical fiber, and the polarization states of the signal light and the local oscillator light are the same, correct coherent reception and demodulation of the optical signal in the first direction can be achieved without adopting a polarization diversity structure, so that the complexity of the device is reduced by half.

If the first-direction optical signal is modulated by Quadrature Phase Shift Keying (QPSK) (without being limited to this modulation format), the second coherent receiver 22 may adopt the structure shown in fig. 15, including a 90 ° mixer 221 and two pairs of balanced detectors 222, where the 90 ° mixer 221 is configured to coherently mix the local oscillator light and the modulated second-wavelength optical signal, and output the coherent light and the modulated second-wavelength optical signal to the two pairs of balanced detectors 222; the two pairs of balanced detectors 222 are configured to demodulate the coherently mixed signals respectively. Compared with the polarization diversity structure, the second coherent receiver 22 only needs to perform frequency mixing and detection in one polarization direction, which saves half of devices and reduces the complexity and cost of the second equipment end equipment. In addition, because the frequency difference between the lambda 1 and the lambda 2 is known and the phase difference is constant, the complexity of a DSP algorithm after coherent reception can be simplified, and the system is simple and easy to implement.

Referring to fig. 16, if amplitude modulation is directly used, the structure of the second coherent receiver 22 can be further simplified, and correct coherent reception and demodulation can be achieved by using only one 2 × 2 coupler and a pair of balanced detectors. In this embodiment, the second coherent receiver 22 includes: a second optical coupler 223 and a pair of balanced detectors 222, where the second optical coupler 223 is configured to perform coherent mixing on the local oscillator light and the modulated second wavelength optical signal, and output the local oscillator light and the modulated second wavelength optical signal to the pair of balanced detectors 222 respectively; the pair of balanced detectors 222 is configured to demodulate the coherently mixed signals respectively.

In another embodiment, the second coherent receiver 22 may also employ the structure of the polarization insensitive or polarization diversity low cost coherent receiver provided in fig. 8. In this embodiment, the second coherent receiver 22 includes: the optical fiber coupler comprises a first optical coupler 121, a polarization beam splitter 122, a first photodetector 123, a second photodetector 124 and a signal processing module 125, wherein the polarization beam splitter 122 is respectively connected with the first optical coupler 121, the first photodetector 123 and the second photodetector 124, and the signal processing module 125 is respectively connected with the first photodetector 123 and the second photodetector 124, wherein the first optical coupler 121 is used for performing coherent mixing on the local oscillator light and the modulated second wavelength optical signal to generate a mixed optical signal; the polarization beam splitter 122 is configured to split the mixed optical signal into two polarized optical signals in two directions, send the polarized optical signal polarized in the X direction to the first photodetector 123, and send the polarized optical signal polarized in the Y direction to the second photodetector 124; the first photodetector 123 is configured to convert the polarized light signal polarized in the X direction into a first electrical signal, and send the first electrical signal to the signal processing module 125; the second photodetector 124 is configured to convert the polarized optical signal polarized in the Y direction into a second electrical signal, and send the second electrical signal to the signal processing module 125; the signal processing module 125 is configured to perform digital signal processing on the first electrical signal and the second electrical signal, so as to demodulate the modulated second wavelength optical signal.

The local oscillator light coherently received by the second coherent receiver 22 end comes from a laser at the first device end, so that the expensive local oscillator laser is saved, and the cost of the second device end device is further reduced.

Referring to fig. 17, taking an application of the embodiment of the present invention to a PON system as an example, the PON system includes: the optical distribution network system comprises local side OLT equipment, terminal ONU equipment and an optical distribution network ODN.

The OLT end equipment sends a downlink optical signal, wherein the downlink optical signal comprises two wavelengths, one wavelength lambda 2(S) is a modulated optical signal, and the other wavelength lambda 1 is direct current light; before the downlink optical signal is output, a modulation and separation subunit 112 in the OLT splits the direct current light into a part, which is used as local oscillator light λ 1(LO) for coherent reception at the OLT end;

the downlink optical signal reaches a certain ONU through an optical splitter in the ODN, a downlink modulation signal λ 2(S) is obtained through filtering by the transceiver subunit 211, and after the direct current light with the wavelength λ 1 is amplified by an optical amplifier in the transceiver subunit 211, part of the light with optical power is split out and is input into the second coherent receiver 22 as the local oscillator light λ 1(LO) and the λ 2(S) modulation optical signal together for coherent mixing, photoelectric conversion, and other processing, so as to realize coherent reception of the downlink signal;

the other part of the direct current light with the wavelength of λ 1 enters the second optical transmitter 212 for modulation and reflection processing to obtain an uplink modulation signal λ 1(S), and then λ 1(S) enters the ODN for transmission;

after the uplink signal light λ 1(S) reaches the OLT, the uplink signal light passes through the interface subunit 113, and is coherently mixed with the local oscillator light λ 1(LO) output by the first optical transmitter 111 through the modulation separation subunit 112, so as to implement coherent reception of the uplink signal.

On the premise of ensuring the OLT output and ONU input signals described in fig. 10, the OLT as the first device provided in fig. 3 to 8 and the ONU as the second device provided in fig. 9 to 16 can be freely combined and cooperate with the ODN to form a coherent reception PON system.

In the low-cost coherent reception PON system provided by the application example of the invention, the local oscillator light coherently received by the uplink and downlink signals is from the laser at the OLT end, so that the use of expensive high-precision tunable lasers at the OLT end and the ONU end is avoided. In addition, the uplink modulation signal is obtained by modulating, reflecting, amplifying and the like the downlink direct current signal, so that a laser for transmitting the uplink signal by the ONU end can be omitted, and the cost of the ONU end equipment is greatly reduced. Two wavelengths are adopted in the downlink direction, one path of signal can be modulated at the same time, one path of signal can be directly used as local oscillator light after passing through an optical amplifier as a direct current signal, and compared with a single-wavelength uplink and downlink scheme, the method avoids the adoption of a complex device to realize the erasure of modulation data. In addition, because the signal light and the local oscillator light of the coherent receiver at the input ONU end come from the same light source and are transmitted through the same optical fiber, and the polarization states of the signal light and the local oscillator light are consistent, the correct coherent reception and demodulation of the downlink signal light can be realized without adopting a polarization diversity structure, so that the complexity of the device is reduced by half. In addition, two wavelengths in the downlink signal come from the same laser, the frequency difference is constant and adjustable, the wavelength of the local oscillation light does not need to be adjusted continuously along with the change of the environment and the temperature, the complexity of the realization of the system and the DSP algorithm is reduced, and the large-scale application is favorably realized. In the uplink direction, as the local oscillation light coherently received by the OLT end comes from the laser of the transmitting end, the expensive high-precision local oscillation laser is saved, and the cost of the OLT end equipment is reduced. The coherent reception of the uplink signal can also adopt a simplified structure of a coherent receiver, thereby reducing the complexity and the cost of the device. In addition, because the wavelengths of the signal light and the local oscillation light are the same, homodyne reception is easy to realize, meanwhile, the complexity of a DSP algorithm is also reduced, and the system is simple and easy to realize.

Referring to fig. 18, a PON system architecture diagram according to another embodiment of the present invention is provided, where the PON system includes: the optical distribution network system comprises local side OLT equipment, terminal ONU equipment and an optical distribution network ODN.

the downlink optical signal reaches a certain ONU through an optical splitter in the ODN, a downlink modulation signal λ 2(S) is obtained through filtering by the transceiver subunit 211, and after the direct current light with the wavelength λ 1 is amplified by an optical amplifier in the transceiver subunit 211, a part of light with optical power is split out and input to the second coherent receiver 22 as local oscillation light λ 1(LO) and λ 2(S) modulation optical signal together for coherent mixing, photoelectric conversion and other processing, so as to realize coherent reception of the downlink signal;

another part of the dc light with the wavelength λ 1 enters the second optical transmitter 212 (including the third modulator 2121 and the faraday rotating mirror 2123) for modulation and reflection processing, so as to obtain an uplink modulation signal λ 1(S), and then λ 1(S) enters the ODN for transmission;

after the uplink signal light λ 1(S) reaches the OLT, the uplink signal light passes through the interface subunit 113 and the polarization rotator 114, and is subjected to coherent mixing with the local oscillator light λ 1(LO) output by the modulation separation subunit 112 by the first optical transmitter 111, so as to implement coherent reception of an uplink signal.

The second optical transmitter 212 in the ONU apparatus of the present application example takes the form of integrally pulling a First Rotating Mirror (FRM) behind the reflective optical modulator as shown in fig. 14 (c). The FRM has the effects that the polarization state of an optical signal rotates by 45 degrees after Faraday rotation for the first time, the polarization state can rotate by 45 degrees again in the same direction after Faraday rotation for the second time after reflection by a reflector, and therefore the polarization state of the input and output optical signals of the FRM can rotate by 90 degrees. From the OLT end, the polarization state of λ 1(LO) may be deflected after transmission through the optical fiber link, and the polarization state is rotated by 90 ° after FRM, and then becomes λ 1(S) after reflection modulation, and after transmission through the same optical fiber link, the polarization rotation caused by the optical fiber link can be cancelled. Therefore, when the influence of the optical modulator on the polarization state is neglected, the polarization states of λ 1(LO) and λ 1(S) coherently received at the OLT end become non-random, and the polarization states of the two become perpendicular to each other. Therefore, the polarization rotator 114 can be used at the OLT end to perform polarization rotation on λ 1(S) or λ 1(LO) to ensure that the polarization states of λ 1(S) and λ 1(LO) entering the coherent receiver are the same, so that the first coherent receiver 12 at the OLT end can realize correct coherent reception and demodulation of the uplink signal light without using a coherent receiver structure of polarization diversity, thereby reducing the complexity of the device by half and further reducing the cost of the equipment at the OLT end. It should be noted that, if the ONU side device adopts a structure with FRM characteristic, the OLT side selects the polarization rotator to cooperate with the ONU side for correct coherent reception.

For the first device side, as shown in fig. 19, the implementation method of coherent detection according to the embodiment of the present invention includes:

step 401, a first device sends a first-direction optical signal to a second device, where the first-direction optical signal includes a direct-current first-wavelength optical signal and a modulated second-wavelength optical signal;

step 402, the first device receives a second-direction optical signal from the second device, uses a part of a direct-current first-direction optical signal in the first-direction optical signal as coherent-received local oscillator light, performs coherent mixing with the second-direction optical signal, and demodulates the second-direction optical signal; wherein the second direction optical signal comprises a modulated first wavelength optical signal.

As shown in fig. 20, in an embodiment, before the first device sends the first-direction optical signal to the second device, the method further includes:

step 501, generating an optical signal to be modulated, where the optical signal to be modulated includes a direct-current first wavelength optical signal and a direct-current second wavelength optical signal;

step 502, modulating a direct-current second wavelength optical signal in the optical signal to be modulated into a modulated second wavelength optical signal, and taking the direct-current first wavelength optical signal and the modulated second wavelength optical signal as optical signals in a first direction.

In an embodiment, the generating an optical signal to be modulated includes:

directly generating the optical signal to be modulated, or

Generating a single-wavelength optical signal, and generating the optical signal to be modulated through the single-wavelength optical signal.

The optical signal to be modulated may be directly generated by a dual-wavelength laser, or a single-wavelength optical signal may be generated by a single-wavelength laser, and the optical signal to be modulated may be generated by the single-wavelength optical signal.

Two wavelengths in the optical signal in the first direction come from the same laser, the frequency difference is constant and adjustable, the wavelength of the local oscillation light does not need to be adjusted continuously along with the change of environment and temperature, the complexity of the realization and the operation of the system is reduced, and the large-scale application is favorably realized.

In an embodiment, the generating the optical signal to be modulated by the single-wavelength optical signal includes:

modulating the single wavelength optical signal to generate the optical signal to be modulated, or

Modulating the single-wavelength optical signal to generate optical signals with more than two wavelengths including the direct-current first-wavelength optical signal and the direct-current second-wavelength optical signal, and filtering the optical signals with more than two wavelengths to obtain the optical signal to be modulated.

Wherein, because the single wavelength laser is the laser that commonly uses, so adopt single wavelength laser can further reduce cost.

As shown in fig. 21, in an embodiment, the modulating a direct-current second-wavelength optical signal in the optical signal to be modulated into a modulated second-wavelength optical signal, and taking the direct-current first-wavelength optical signal and the modulated second-wavelength optical signal as first-direction optical signals includes:

step 601, dividing the optical signal to be modulated into two paths of light beams, wherein one path of light beam is a direct-current first-wavelength optical signal, and the other path of light beam is a direct-current second-wavelength optical signal;

step 602, modulating the direct-current second wavelength optical signal into a modulated second wavelength optical signal;

step 603, combining the direct-current first wavelength optical signal and the modulated second wavelength optical signal into a light beam, which is used as an optical signal in the first direction.

The optical signal to be modulated can be divided into two paths of light beams by using a wave splitter, the direct-current second-wavelength optical signal is modulated into the modulated second-wavelength optical signal by using an optical modulator, and the direct-current first-wavelength optical signal and the modulated second-wavelength optical signal are combined into one path of light beam by using a wave combiner.

As shown in fig. 22, in an embodiment, the performing coherent mixing on a part of a direct-current first-wavelength optical signal in the first-direction optical signal and the second-direction optical signal as coherently received local oscillation light to demodulate the second-direction optical signal includes:

step 701, performing coherent mixing on a part of the direct-current first wavelength optical signal in the first-direction optical signal, which is used as coherent received local oscillation light, and the second-direction optical signal to generate a mixed optical signal;

step 702, dividing the mixed optical signal into two directions of polarized optical signals, converting the two directions of polarized optical signals into electrical signals, and performing digital signal processing on the electrical signals, thereby demodulating the optical signals in the second direction.

The coherent reception can adopt a polarization insensitive coherent receiver structure, and can realize correct coherent reception and demodulation of the optical signal in the second direction without adopting a polarization diversity structure and a complex DSP algorithm, so that the complexity of the device is greatly reduced, and the cost of the equipment is further reduced.

In an embodiment, before performing coherent mixing on the local oscillator light and the optical signal in the second direction when the optical signal in the second direction received by the first device is an optical signal subjected to polarization processing, the method further includes: and carrying out polarization processing on the received optical signal in the second direction.

The polarization rotator can be adopted to perform polarization processing on the received optical signal in the second direction, so that the local oscillation light entering the coherent receiver and the optical signal in the second direction have the same polarization state, and the coherent receiver can realize correct coherent reception and demodulation of the uplink signal light without adopting a coherent receiver structure of polarization diversity, so that the complexity of the device is reduced by half, and the cost of the OLT end equipment is further reduced.

For the second device, as shown in fig. 23, the implementation method of coherent detection according to the embodiment of the present invention includes:

step 801, a second device receives a first-direction optical signal from a first device, where the first-direction optical signal includes a direct-current first-wavelength optical signal and a modulated second-wavelength optical signal;

step 802, the second device performs coherent mixing on a part of the direct-current first wavelength optical signal as coherent received local oscillation light and the modulated second wavelength optical signal, and demodulates the modulated second wavelength optical signal.

As shown in fig. 24, in an embodiment, the method further comprises:

step 803, modulating another part of the direct-current first-wavelength optical signal to generate a modulated first-wavelength optical signal, and sending the modulated first-wavelength optical signal as a second-direction optical signal to the first device.

In the embodiment of the invention, a laser for transmitting the optical signal in the second direction does not need to be additionally arranged, so that the cost of the system is greatly reduced.

In an embodiment, before the second device uses a part of the direct-current first wavelength optical signal as coherent received local oscillation light, the method further includes:

power amplifying the first direction optical signal, or

And dividing the optical signal in the first direction into two paths of light beams, wherein one path of light beam is a direct-current first wavelength optical signal, the other path of light beam is a modulated second wavelength optical signal, and performing power amplification on the direct-current first wavelength optical signal.

The optical signal in the first direction can be amplified first, and then divided into a direct-current first wavelength optical signal by a wave divider, and the other path of optical beam is a modulated second wavelength optical signal; or the optical signal in the first direction may be first divided into two light beams by the splitter, and only the direct-current optical signal in the first wavelength may be amplified.

In an embodiment, before modulating another part of the direct-current first-wavelength optical signal to generate a modulated first-wavelength optical signal, the method further includes:

and performing regenerative amplification on the other part of the direct-current first-wavelength optical signal.

Wherein another part of the direct current first wavelength optical signal can be regeneratively amplified by an injection locked FP laser.

In an embodiment, the performing, by the second device, coherent mixing on a part of the direct-current first-wavelength optical signal as coherent-received local oscillation light and the modulated second-wavelength optical signal, and demodulating the modulated second-wavelength optical signal includes:

taking a part of direct-current first wavelength optical signals in the first direction optical signals as coherent received local oscillation light, and performing coherent mixing with the modulated second wavelength optical signals to generate four or two paths of mixed optical signals;

and demodulating the four or two paths of mixed frequency optical signals.

The signal light and the local oscillator light at the second equipment end come from the same laser, and the polarization state of the local oscillator light can be kept consistent with that of the signal light, so that the correct coherent reception and demodulation can be realized without adopting a polarization diversity structure in the coherent reception in the first direction, and the complexity and the cost of devices are reduced. In addition, because coherent reception is carried out on the signal light and the local oscillator light with correlation, the generation of phase noise can be effectively inhibited, the frequency difference is known, and the phase difference is constant, the back end of a coherent receiver does not need to adopt a complex Digital Signal Processing (DSP) algorithm, the system structure is simple, and the cost is low.

In an embodiment, before the transmitting the modulated optical signal of the first wavelength as the optical signal of the second direction to the first device, the method further includes:

and carrying out polarization processing on the modulated first wavelength optical signal.

The faraday rotating mirror can be used for carrying out polarization processing on the modulated first wavelength optical signal, so that the polarization state of the local oscillator light entering the coherent receiver in the first device is the same as that of the second direction optical signal, and the coherent receiver does not need to adopt a coherent receiver structure of polarization diversity.

As for the implementation system of coherent detection, as shown in fig. 25, the implementation method of coherent detection according to the embodiment of the present invention includes:

step 901, a first device sends a first-direction optical signal to a second device, where the first-direction optical signal includes a direct-current first-wavelength optical signal and a modulated second-wavelength optical signal;

step 902, the second device receives the first-direction optical signal from the first device, performs coherent mixing on a part of the direct-current first-wavelength optical signal as coherent received local oscillation light and the modulated second-wavelength optical signal, and demodulates the modulated second-wavelength optical signal.

In one embodiment, as shown in fig. 26, the method further comprises:

step 903, the second device modulates another part of the direct-current optical signal with the first wavelength to generate a modulated optical signal with the first wavelength, and sends the modulated optical signal with the first wavelength to the first device as an optical signal in a second direction;

step 904, the first device receives a second-direction optical signal from the second device, performs coherent mixing with the second-direction optical signal by using a part of the direct-current first-wavelength optical signal in the first-direction optical signal as coherent received local oscillation light, and demodulates the second-direction optical signal.

In the embodiment of the invention, the local oscillator light coherently received by the signals in the two directions is from the laser at the first equipment end, so that the condition that the high-precision tunable lasers with high price are used by the equipment at the two ends is avoided. And moreover, a laser for transmitting the optical signal in the second direction does not need to be additionally configured, so that the cost of the system is greatly reduced.

For the implementation system of coherent detection, the implementation method of coherent detection according to the embodiments of the present invention may be implemented with reference to the foregoing embodiments, and details are not described here.

It will be understood by those of ordinary skill in the art that all or some of the steps of the methods, systems, functional modules/units in the devices disclosed above may be implemented as software, firmware, hardware, and suitable combinations thereof. In a hardware implementation, the division between functional modules/units mentioned in the above description does not necessarily correspond to the division of physical components; for example, one physical component may have multiple functions, or one function or step may be performed by several physical components in cooperation. Some or all of the components may be implemented as software executed by a processor, such as a digital signal processor or microprocessor, or as hardware, or as an integrated circuit, such as an application specific integrated circuit. Such software may be distributed on computer readable media, which may include computer storage media (or non-transitory media) and communication media (or transitory media). The term computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data, as is well known to those of ordinary skill in the art. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, Digital Versatile Disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can accessed by a computer. In addition, communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media as known to those skilled in the art.

Claims

1. An apparatus for implementing coherent detection, comprising:

a first coherent receiver, connected to the first transceiver, configured to perform coherent mixing on a part of a direct-current first wavelength optical signal in the first direction optical signal as coherent received local oscillation light and the second direction optical signal, and demodulate the second direction optical signal;

the first transceiving unit comprises a first optical transmitter; the first optical transmitter is configured to generate an optical signal to be modulated, where the optical signal to be modulated includes the direct-current first wavelength optical signal and the direct-current second wavelength optical signal.

2. The apparatus of claim 1, wherein the first transceiver unit further comprises a modulation separation subunit and an interface subunit, the first optical transmitter, the modulation separation subunit and the interface subunit being connected in sequence, wherein

The modulation separation subunit is configured to modulate a direct-current second wavelength optical signal in the optical signal to be modulated into a modulated second wavelength optical signal;

the interface subunit is configured to send a first-direction optical signal to a second device by using a direct-current first-wavelength optical signal and a modulated second-wavelength optical signal as first-direction optical signals, receive a second-direction optical signal from the second device, and send the second-direction optical signal to the first coherent receiver.

3. The apparatus of claim 2, wherein the modulation separation subunit comprises a first splitter, a first optical modulator, and a combiner connected in series, wherein

The first wave splitter is used for splitting the optical signal to be modulated into two paths of light beams, wherein one path of light beam is a direct-current first wavelength optical signal, and the other path of light beam is a direct-current second wavelength optical signal; sending one part of the direct-current light beam with the first wavelength to the first coherent receiver, and sending the other part of the direct-current light beam with the first wavelength to the combiner; sending the direct-current light beam with the second wavelength optical signal to the first optical modulator;

the first optical modulator is configured to modulate the received direct-current second wavelength optical signal into a modulated second wavelength optical signal, and send the modulated second wavelength optical signal to the combiner;

the combiner is configured to combine the received dc first wavelength optical signal and the modulated second wavelength optical signal into a light beam, and send the light beam to the interface subunit.

4. The apparatus of claim 2, wherein the first optical transmitter comprises a dual-wavelength laser,

the dual-wavelength laser is used for generating the optical signal to be modulated.

5. The apparatus of claim 2, wherein the first optical transmitter comprises a single wavelength laser, a radio frequency source, and a second optical modulator, wherein the single wavelength laser is coupled to the second optical modulator, and the second optical modulator is coupled to the radio frequency source and the modulation splitting subunit, respectively;

the single-wavelength laser is used for generating a single-wavelength optical signal and sending the single-wavelength optical signal to the second optical modulator;

the second optical modulator is configured to modulate the single-wavelength optical signal under the driving of the radio frequency source, generate the optical signal to be modulated, and send the optical signal to the modulation and separation subunit.

6. The apparatus of claim 2, wherein the first optical transmitter comprises a single wavelength laser, a radio frequency source, a second optical modulator, and a tunable filter, wherein the single wavelength laser is coupled to the second optical modulator, the second optical modulator is coupled to the radio frequency source and the tunable filter, respectively, and the tunable filter is coupled to the modulation splitting subunit;

the second optical modulator is configured to modulate the single-wavelength optical signal under driving of the radio frequency source, and generate optical signals with two or more wavelengths including the direct-current first-wavelength optical signal and the direct-current second-wavelength optical signal;

the tunable filter is configured to filter the optical signals with the two or more wavelengths to obtain the optical signal to be modulated, and send the optical signal to the modulation separation subunit.

7. The apparatus of claim 2,

the interface subunit includes an optical circulator.

8. The apparatus according to any one of claims 2 to 7, wherein the first transceiver unit further comprises a polarization rotator,

and the polarization rotator is respectively connected with the first coherent receiver and the interface subunit, and is used for performing polarization conversion on the optical signal in the second direction and sending the optical signal to the first coherent receiver.

9. The apparatus of any of claims 1-7, wherein the first coherent receiver comprises: the photoelectric detector comprises a first optical coupler, a polarization beam splitter, a first photoelectric detector, a second photoelectric detector and a signal processing module, wherein the polarization beam splitter is respectively connected with the first optical coupler, the first photoelectric detector and the second photoelectric detector, the signal processing module is respectively connected with the first photoelectric detector and the second photoelectric detector, and the polarization beam splitter is connected with the first photoelectric detector and the second photoelectric detector

The first optical coupler is used for performing coherent frequency mixing on the local oscillator light and the optical signal in the second direction to generate a path of frequency mixing optical signal;

the polarization beam splitter is configured to split the mixed optical signal into polarized optical signals in two directions, send the polarized optical signal polarized in the X direction to the first photodetector, and send the polarized optical signal polarized in the Y direction to the second photodetector;

the first photoelectric detector is used for converting the polarized light signal polarized in the X direction into a first electric signal and sending the first electric signal to the signal processing module;

the second photoelectric detector is used for converting the polarized light signal polarized in the Y direction into a second electric signal and sending the second electric signal to the signal processing module;

the signal processing module is configured to perform digital signal processing on the first electrical signal and the second electrical signal, so as to demodulate the second direction optical signal.

10. An apparatus for implementing coherent detection, comprising:

a second coherent receiver, connected to the second transceiver unit, configured to perform coherent mixing on a part of the direct-current first wavelength optical signal as coherent received local oscillation light and the modulated second wavelength optical signal, and demodulate the modulated second wavelength optical signal;

the second transceiver unit is further configured to modulate another part of the direct-current first-wavelength optical signal, generate a modulated first-wavelength optical signal, and send the modulated first-wavelength optical signal to the first device as a second-direction optical signal.

11. The apparatus of claim 10, wherein the second transceiver unit comprises: a transceiver sub-unit and a second optical transmitter connected, wherein

The transceiver sub-unit is configured to receive a first-direction optical signal from a first device, send a part of the direct-current first-wavelength optical signal to the second coherent receiver, and send another part of the direct-current first-wavelength optical signal to the second optical transmitter; receiving the modulated first wavelength optical signal sent by the second optical transmitter, and sending the modulated first wavelength optical signal to the first device;

and the second optical transmitter is configured to modulate another part of the direct-current first-wavelength optical signal to generate a modulated first-wavelength optical signal.

12. The apparatus of claim 11, wherein the transceiver sub-unit comprises a signal splitting and amplifying module, the signal splitting and amplifying module comprising a second splitter and an optical amplifier connected thereto, wherein

The second wave splitter is configured to split the optical signal in the first direction into two light beams, where one light beam is a direct-current first wavelength optical signal, and the other light beam is a modulated second wavelength optical signal; sending the direct-current first wavelength optical signal to the optical amplifier; sending the modulated second wavelength optical signal to the second coherent receiver;

the optical amplifier is configured to perform power amplification on the direct-current first-wavelength optical signal, send a part of the amplified direct-current first-wavelength optical signal to the second coherent receiver as coherent received local oscillation light, and output the other part of the amplified direct-current first-wavelength optical signal to the second optical transmitter.

13. The apparatus of claim 12, wherein the transceiver sub-unit comprises a signal splitting and amplifying module comprising an optical amplifier and a second splitter coupled together, wherein

The optical amplifier is used for performing power amplification on the first direction optical signal and outputting the first direction optical signal to the second wave splitter;

the second wave splitter is configured to split the amplified first-direction optical signal into two light beams, where one light beam is a direct-current first-wavelength optical signal, and the other light beam is a modulated second-wavelength optical signal; outputting a part of the direct-current first-wavelength optical signal to the second coherent receiver as coherent-received local oscillation light, and outputting the other part of the direct-current first-wavelength optical signal to the second optical transmitter; outputting the modulated second wavelength optical signal to the second coherent receiver.

14. The apparatus of claim 12 or 13, wherein the transceiver subunit further comprises a first interface module and a second interface module, wherein

The first interface module is configured to output the optical signal in the first direction to the signal separation and amplification module, and send the modulated optical signal in the first direction to the first device as an optical signal in a second direction;

the second interface module is configured to output the direct-current first wavelength optical signal output by the signal separation and amplification module to the second optical transmitter, and output the modulated first wavelength optical signal output by the second optical transmitter to the first interface module.

15. The apparatus of claim 14,

the first interface module and the second interface module both comprise optical circulators.

16. The apparatus of claim 11,

the second optical transmitter includes a third optical modulator, which is a reflective optical modulator.

17. The apparatus of claim 11, wherein the second optical transmitter comprises a fabry-perot FP laser and a third optical modulator, wherein

The FP laser is an injection locking laser and is used for regenerating and amplifying an input optical signal according to the frequency of the input direct-current first wavelength optical signal;

and the third optical modulator is respectively connected with the FP laser and the transceiver subunit, and is used for modulating the amplified direct-current first wavelength optical signal and outputting the modulated first wavelength optical signal.

18. The apparatus of claim 16, wherein the second optical transmitter further comprises a faraday rotator mirror, and wherein

And the Faraday rotation reflector is connected with the third optical modulator and is used for carrying out polarization processing on the modulated first wavelength optical signal output by the third optical modulator and outputting the modulated first wavelength optical signal subjected to polarization processing to the third optical modulator.

19. The apparatus of claim 10, wherein the second coherent receiver comprises: the device comprises a first optical coupler, a polarization beam splitter, a first photoelectric detector, a second photoelectric detector and a signal processing module, wherein the polarization beam splitter is respectively connected with the first optical coupler, the first photoelectric detector and the second photoelectric detector, the signal processing module is respectively connected with the first photoelectric detector and the second photoelectric detector, and the polarization beam splitter is connected with the first photoelectric detector, the second photoelectric detector and the signal processing module

The first optical coupler is configured to perform coherent frequency mixing on the local oscillator light and the modulated second wavelength optical signal to generate a mixed optical signal;

the signal processing module is configured to perform digital signal processing on the first electrical signal and the second electrical signal, so as to demodulate the modulated optical signal with the second wavelength.

20. The apparatus of claim 10, wherein the second coherent receiver comprises: a 90 DEG mixer and two pairs of balanced detectors, wherein

The 90 ° frequency mixer is configured to perform coherent frequency mixing on the local oscillator light and the modulated second wavelength optical signal, and output the local oscillator light and the modulated second wavelength optical signal to the two pairs of balanced detectors respectively;

and the two pairs of balanced detectors are used for demodulating the signals after the coherent mixing respectively.

21. The apparatus of claim 10, wherein the second coherent receiver comprises: a second optical coupler and a pair of balanced detectors, wherein

The second optical coupler is used for performing coherent mixing on the local oscillator light and the modulated second wavelength optical signal and outputting the two signals to the pair of balanced detectors respectively;

and the pair of balanced detectors is used for demodulating the signals after the coherent mixing respectively.

22. The system for realizing coherent detection is characterized by comprising a first device and a second device connected with the first device through an optical fiber link, wherein the first device and the second device are connected through the optical fiber link

The first device comprises a coherent detection apparatus as claimed in any one of claims 1 to 9;

the second apparatus comprising a coherent detection device as claimed in any one of claims 10 to 21.

23. A method for realizing coherent detection comprises the following steps:

the first device receives a second-direction optical signal from the second device, performs coherent mixing on a part of a direct-current first-direction optical signal in the first-direction optical signal as coherent-received local oscillation light and the second-direction optical signal, and demodulates the second-direction optical signal; wherein the second directional optical signal comprises a modulated first wavelength optical signal;

before the first device sends the first-direction optical signal to the second device, the method further includes:

and generating an optical signal to be modulated, wherein the optical signal to be modulated comprises a direct-current first wavelength optical signal and a direct-current second wavelength optical signal.

24. The method of claim 23, wherein prior to the first device transmitting the first direction optical signal to the second device, further comprising:

and modulating a direct-current second wavelength optical signal in the optical signals to be modulated into a modulated second wavelength optical signal, and taking the direct-current first wavelength optical signal and the modulated second wavelength optical signal as first direction optical signals.

25. The method of claim 24, wherein the generating an optical signal to be modulated comprises:

directly generating the optical signal to be modulated, or

26. The method of claim 25, wherein said generating the optical signal to be modulated from the single wavelength optical signal comprises:

27. The method of claim 24, wherein the modulating the direct-current second-wavelength optical signal into the modulated second-wavelength optical signal, and taking the direct-current first-wavelength optical signal and the modulated second-wavelength optical signal as the first-direction optical signal, comprises:

dividing the optical signal to be modulated into two paths of light beams, wherein one path of light beam is a direct-current first wavelength optical signal, and the other path of light beam is a direct-current second wavelength optical signal;

modulating the direct-current second wavelength optical signal into a modulated second wavelength optical signal;

and combining the direct-current first wavelength optical signal and the modulated second wavelength optical signal into a light beam as a first direction optical signal.

28. The method of claim 23, wherein the coherently mixing a portion of the direct first wavelength optical signal in the first direction optical signal with the second direction optical signal as coherently received local oscillator light to demodulate the second direction optical signal, comprising:

taking a part of a direct-current first-wavelength optical signal in the first-direction optical signal as coherent-received local oscillation light, and performing coherent mixing with the second-direction optical signal to generate a mixed optical signal;

and dividing the mixed optical signal into polarized optical signals in two directions, converting the polarized optical signals in the two directions into electric signals, and performing digital signal processing on the electric signals so as to demodulate the optical signals in the second direction.

29. The method according to any one of claims 23 to 28, wherein when the second-direction optical signal received by the first device is a polarization-processed optical signal, before performing coherent mixing on the local oscillator light and the second-direction optical signal, the method further includes:

and carrying out polarization processing on the received optical signal in the second direction.

30. A method for realizing coherent detection comprises the following steps:

the second device performs coherent mixing on a part of the direct-current first-wavelength optical signal as coherent received local oscillation light and the modulated second-wavelength optical signal, and demodulates the modulated second-wavelength optical signal;

and modulating another part of the direct-current first-wavelength optical signal to generate a modulated first-wavelength optical signal, and sending the modulated first-wavelength optical signal as a second-direction optical signal to the first device.

31. The method of claim 30, wherein before the second device treats a portion of the dc first wavelength optical signal as coherently received local oscillator light, the method further comprises:

power amplifying the first direction optical signal, or

32. The method of claim 30 wherein, prior to modulating another portion of the direct current first wavelength optical signal to produce a modulated first wavelength optical signal, the method further comprises:

and regenerating and amplifying the other part of the direct-current first-wavelength optical signal.

33. The method of claim 30, wherein the second device coherently mixes a portion of the direct current first wavelength optical signal with the modulated second wavelength optical signal as coherently received local oscillator light, and demodulates the modulated second wavelength optical signal, comprising:

and demodulating the four or two paths of mixed frequency optical signals.

34. A method as claimed in any one of claims 30 to 32, wherein prior to sending the modulated optical signal of the first wavelength as a second direction optical signal to the first device, the method further comprises:

35. A method for realizing coherent detection comprises the following steps:

a first device sends a first direction optical signal to a second device, wherein the first direction optical signal comprises a direct current first wavelength optical signal and a modulated second wavelength optical signal; before the first device sends the first-direction optical signal to the second device, the method further includes: generating an optical signal to be modulated, wherein the optical signal to be modulated comprises a direct-current first wavelength optical signal and a direct-current second wavelength optical signal;

the second device receives a first-direction optical signal from the first device, performs coherent mixing on a part of the direct-current first-wavelength optical signal as coherent received local oscillation light and the modulated second-wavelength optical signal, and demodulates the modulated second-wavelength optical signal;

the second device modulates another part of the direct-current first-wavelength optical signal to generate a modulated first-wavelength optical signal, and sends the modulated first-wavelength optical signal to the first device as a second-direction optical signal;

the first device receives a second direction optical signal from the second device, performs coherent mixing with the second direction optical signal by using a part of a direct-current first wavelength optical signal in the first direction optical signal as coherent received local oscillation light, and demodulates the second direction optical signal.